Generally, an ink cartridge that is a removable liquid reservoir is attached to an ink-jet type printing device that is an example of the liquid consumption device. One type of the ink cartridge has a prism to optically detect a remaining state of ink in the inside. For example, in Patent Document 1, a prism is provided in an ink cartridge of a printing device, and a remaining state of ink is optically detected. Also, by providing a reflective member to be aligned with the prism of the ink cartridge and emitting light thereto, a boundary position between the reflective member and sections other than the reflective member is calculated. Then, based on the calculated boundary position, the position of the prism is corrected, so that reflected light from the prism can be received in a correct position.